1. Field of the Invention
The present invention concerns an automatic transmission in the form of a belt-driven conical-pulley transmission, such as is known, for example, from DE 10 2004 015 215 and other publications, as well as to a method for controlling and/or operating it and a vehicle equipped with it.
2. Description of the Related Art
Automatic transmissions in the broader sense are converters, whose momentary transmission ratio changes automatically, in steps or continuously, as a function of present or anticipated operating conditions, such as partial load, and thrust and environmental parameters, such as temperature, air pressure, and humidity. They include converters that are based on an electrical, pneumatic, hydrodynamic, or hydrostatic principles, or on a principle that is a mixture of those principles.
The automation refers to a variety of functions, such as start-up, choice of transmission ratio, or type of transmission ratio change in various operating situations, where the type of transmission ratio change can mean, for example shifting, to different gear levels in sequence, skipping gear levels, and the speed of shifting.
The desire for convenience, safety, and reasonable construction expense determines the degree of automation, i.e., how many functions run automatically.
As a rule, the driver can intervene manually in the automatic sequence, or can limit it for individual functions.
Automatic transmissions in the narrower sense, as they are used today primarily in the construction of motor vehicles, usually have the following structure:
On the input side of the transmission there is a start-up unit in the form of a regulatable clutch, for example a wet or dry friction clutch, a hydrodynamic clutch, or a hydrodynamic converter.
With a hydrodynamic converter, often a lock-up clutch is connected in parallel with the pump and turbine parts, which increases the efficiency by transmitting the force directly and damps the oscillations through defined slippage at critical rotational speeds.
The start-up unit drives a mechanical, continuously adjustable or stepped multi-speed gearbox, which can include a forward/reverse drive unit, a main gear group, a range gear group, a split gear group, and/or a variable speed drive unit. Transmission gear groups can be of intermediate gear or planetary design, with spur or helical tooth system, as a function of the requirements in terms of quietness of operation, space conditions, and transmission ratio options.
The output element of the mechanical transmission, a shaft or a gear, drives a differential, directly or indirectly, via intermediate shafts or an intermediate stage with a constant transmission ratio. The differential can be configured as a separate gearbox or as an integral component of the automatic transmission. In principle, the transmission is suitable for longitudinal or transverse installation in the vehicle.
To adjust the transmission ratio in the mechanical transmission there are provided hydrostatic, pneumatic, and/or electrical actuators. A hydraulic pump, which operates by the displacement principle, supplies oil under pressure for the start-up unit, in particular the hydrodynamic unit, for the hydrostatic actuators of the mechanical transmission, and for lubricating and cooling the system. Depending upon the necessary pressure and delivery volume, possibilities include gear pumps, screw pumps, vane pumps, and piston pumps, the latter usually of radial design. In practice, gear pumps and radial piston pumps have come to predominate for that purpose, with gear pumps offering advantages because they are less expensive to build, and radial piston pumps offering advantages because of their higher pressure level and better ability to be regulated.
The hydraulic pump can be located at any desired position in the transmission, on a main or a secondary shaft that is constantly driven by the drive unit.
Continuously adjustable automatic transmissions are known that consist of a start-up unit, a reversing planetary gearbox as the forward/reverse drive unit, a hydraulic pump, a variable speed drive unit, an intermediate shaft and a differential. The variable speed drive unit in turn is made up of two pairs of conical disks and an endless torque-transmitting means. Each pair of conical disks includes a second conical disk that is displaceable in the axial direction. Between the pairs of conical disks runs the endless torque-transmitting means, which can be, for example, a thrust element belt, a tension chain, or a strap belt. Moving the second conical disk changes the running radius of the endless torque-transmitting means, and thus the transmission ratio of the continuously adjustable automatic transmission.
Continuously adjustable automatic transmissions require a high pressure level in order to be able to adjust the conical disks of the variable speed drive unit with the desired speed at all operating points, and also to transmit the torque with sufficient basic pressure with minimum wear.
One object of the present invention is to increase the operational strength of the components and thus to prolong the operating life of such an automatic transmission. A further object of the present invention is to increase the torque transmission capability of such a transmission and to be able to transmit higher forces through the components of the transmission. Furthermore, hence another object, such a transmission should be cost-effectively producible.
Another object of the invention is to be able to move the variable speed drive unit of a belt-driven conical-pulley transmission at the highest possible speed, i.e., to achieve the maximum adjustment between underdrive and overdrive, or vice versa, as quickly as possible. In the previously known continuously variable vehicle transmissions, in particular in transmissions having an endless torque-transmitting means, the quick adjustment proceeds in most cases in such away that a quick transmission ratio adjustment is typically transmission ratio regulated. But that transmission-ratio-regulated operation must take account of the former type of regulation itself. In order to prevent oscillations, one must normally put up with sacrifices in the adjustment dynamics, i.e., a slowing of the adjustment, because for reasons of stability the maximum force cannot be utilized during the entire adjustment process.
Furthermore, the speed of adjustment must be reduced before the stops are reached, since the latter cannot be approached with high dynamics, and are also unable to assume the necessary retardation process themselves. In particular in transmissions such as, for example, a concept in which a CVT transmission is operated in combination with an automated shift transmission or a stepped automatic transmission that is connected in series with it, it is important when shifting to be able to adjust the CVT part of the transmission as quickly as possible.
The several objects are achieved by the invention presented in the claims and the description and explained in connection with the figures, along with its refinements.